Education spokesman Christopher Pyne said the Coalition would repeal the Gonski plan if it wins the election and a majority of states have not signed up. The Global Mail. Photograph: Mike Bowers

The Coalition is refusing to state a position on the government's Gonski school funding reform as it waits to see how many states sign up by prime minister Julia Gillard's 30 June deadline.

The Coalition waved the Australian Education Bill through the lower house last month and on Tuesday MPs and senators agreed to leave the Coalition position "open" – giving the leadership group "flexibility" to decide how Liberal and National senators will vote "depending on how events move".

Education spokesman Christopher Pyne has said the Coalition will only continue with the plan if an "overwhelming" majority of states have agreed to it. He has not defined what would constitute an "overwhelming majority".

If the Coalition wins the election and a majority of states have not signed on, Pyne says he will seek to repeal the new funding deal. But with Labor and the Greens still in control of the upper house until next July, a repeal is likely to fail. That would leave the Coalition presiding over the existing funding agreement for some states and the more generous new funding system for others.

So far NSW, the ACT and South Australia have signed deals with the Commonwealth. Victoria and Tasmania are reportedly considering deals. Western Australia turned down a dramatically increased offer from Gillard last week.

The extent to which the new system is more generous is also hotly disputed.

The government says schools stand to lose $16.3 billion if they don't sign the deal, but the Coalition disputes this figure because it says it is based on a comparison with an artificially low "status quo" figure.

The dispute over funding centres on the level of indexation – or annual increase – for schools funding. Under the existing system indexation for federal funding is linked to what state governments pay. In recent years it has averaged 6%. But after recent state government funding cuts it has fallen in 2013 to 3.9% and is anticipated to be 3% next year.

The government has assumed those lower levels of indexation will continue and has compared its new funding offer to the states with this benchmark to calculate how much states will "lose" if the Coalition sticks with the existing system. The Coalition says this is an unfair assumption.

But the Coalition has not announced its own long-term education policy, saying it would "roll over" the existing system for two years and then negotiate a new deal with the states.

The budget shows the extra money Labor is offering for schools ramps up slowly and in the early years is mostly found by redirecting federal funding that had been set aside for so-called "national partnership agreements" – special funding deals for things like improving literacy or numeracy or rewarding the best teachers.

In fact, after the redirections are taken into account, the increase in federal funding is slightly lower in the first two years than it was predicted to be in last year's budget – hence the Coalition's claim that funding has been "cut".

But Labor is proposing billions of dollars in extra schools funding in subsequent years – which it proposes to pay for by cutting the baby bonus and closing corporate tax loopholes.

This huge increase in future resources is presumably what NSW Liberal premier Barry O'Farrell was referring to when he said Gonski was "a once in a generation opportunity for NSW schools" and provided "more resources and fairer distribution" of Commonwealth money.